Wet multi-disc brakes are used in various on and off highway vehicles. They are isolated from environmental dirt and are typically liquid cooled by oil. Often they are integrated directly into transmissions. Heavy tracked vehicles such as earth moving equipment or military armored vehicles typically have transmissions that have two output shafts, one for each track. Brakes are located at each of these outputs. The brakes may be used as service brakes to stop the vehicle or as steering devices to facilitate “skid steer” or both.
In order to slow or steer a tracked vehicle, a great deal of power must be dissipated. The power is usually converted to heat when the brake friction disks make contact with the reaction disks. The heat is removed by oil which is circulated to an oil-to-air cooler and the heat is then removed to the environment.
A brake designer is faced with many challenges including reducing weight and size as well as keeping parasitic losses to a minimum. The brakes must be small enough to fit into the vehicle, yet must have adequate cooling capacity to dissipate the heat generated from braking. Often, the available coolant flow is limited in order to keep auxiliary hydraulics small and to minimize flow losses. Although fully submerging the brake pack (e.g. in a sump) will provide the best cooling environment for the brake disk pack, drag losses created when the brakes are not energized will be unacceptably high. Most wet brake systems are therefore run above the oil level and are sprayed with oil either continuously or intermittently, and only during and for a short time after the braking event.
Various conventional brake systems, including the aforementioned, are disclosed in, for example, “Brake Technology Handbook” by Bert Breuer and Karlheinz H. Bill, published by SAE International, 2008, ISBN 978-0-7680-1787-8.
Notwithstanding the progress made to date using these more efficient cooled braking systems based on intermittent oil spray to the disc packs, there is a continuing need to improve brake performance with regards to energy and power dissipation while minimizing wear and without decreasing vehicle efficiency and/or without increasing the demand from the cooling system. The present invention addresses these and other needs as described below.